Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 072329

National Weather Service Sioux Falls SD
529 PM CST Sun Mar 7 2021

.SHORT TERM...(This Evening through Monday)
Issued at 234 PM CST Sun Mar 7 2021

Temperatures/winds/RH remain the primary focus over the next 24
hours. Boundary approaching I-29 corridor early this afternoon,
and will slowly push east of the area tonight. Gusty winds are
expected to decouple rather quickly this evening, so looking for
light winds tonight as surface ridge moves across the region. With
the dry air mass in place, will hedge lows toward the lower end
of guidance to expand diurnal range.

Surface ridge moves through the Upper Mississippi Valley into the
western Great Lakes Monday, while a weak surface low develops over
the western High Plains. This leaves our region in east-southeast
low level flow much of the day, possibly turning more southerly
toward the Missouri River Valley late. As was seen on Saturday,
southeast tends to be a less favorable wind direction for strong
mixing in our area, so have tempered highs a bit from previous
forecast. Still above the NBM & NBM 50th percentile, but holding a
few degrees shy of the 75th. This still yields highs ranging from
lower 60s in southwest MN, to lower 70s in south central SD, though.
Not quite reaching record highs in most areas, but still acceptable
for early March!

Not only could the southeast flow limit forecast highs slightly, but
should also inhibit the mixing down of sharply drier air as we have
seen when winds have swung around to a more westerly component the
past couple of days. That said, should still see RH fall to around
30% or lower along/west of the James River Valley on Monday. The
southeast winds will be stronger in that same area, farthest from
the surface ridge, with gusts to 30mph possible. So still looking at
High to Very High grassland fire danger across the forecast area,
highest west of I-29.

.LONG TERM...(Monday Night through Sunday)
Issued at 234 PM CST Sun Mar 7 2021

Will see one more very warm early March day on Tuesday, and with
south-southwest winds ahead of the boundary, low level temperatures
do support pushing blended highs toward the 75th percentile of the
NBM once again. This will be our best chance to set new records,
with forecast highs in the 70s most areas. Could also see some new
record high minimum temperatures for March 9th, as stout southerly
flow holds lows in the 40s-near 50, but will have to watch timing of
the cool air behind the boundary to see if the warm morning lows
hold through midnight Tuesday night.

This boundary largely expected to push through dry, however, with
warmth and moisture building ahead of the front, could see a stray
shower or thunderstorm pop across northwest Iowa Tuesday evening.
Chances for precipitation increase further later Tuesday night into
Wednesday/Wednesday night, as a strengthening northern stream wave
slides east out of the Rockies and begins interacting with the low
and mid level frontal boundaries. Still some uncertainty regarding
where the various boundaries will be located, and it`s possible that
our forecast area could see a relative minimum in precip totals with
this midweek system, falling between showers/storms near and south
of the surface front, and a band of rain-turning-to-snow along the
mid level front from western to northeast SD. Should be able to
squeeze out a little light precip between these two more focused
areas, but confidence not high enough to push pops beyond chance
range for most of the forecast area just yet. Expect mainly rain
across our forecast area, but northwest portions of the forecast
area, generally north of Chamberlain-Madison SD-Marshall MN line
could be brushed by a little light snow.

Given aforementioned uncertainty in boundary placement Wednesday,
did not alter NBM high temperatures, though given a tightening low
level thermal gradient in the models, would not be surprised to see
a broader range of highs across our area than the current lower-mid
40s to near 60.

More seasonable air will settle into the region for the latter half
of this week, but without substantial snow cover, temperatures will
likely remain on the warm side of normal. Next system of note will
be a southern stream wave which becomes a cutoff low near the Four
Corners region on Friday, then ejects into the Plains next weekend.
Not a lot of consensus on this system yet, except that it should
track south of our forecast area. That said, could see some light
precip spread northward into parts of our region by Saturday night
or Sunday.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 528 PM CST Sun Mar 7 2021

VFR conditions are forecast to prevail this TAF cycle. Aside from a
bit of cirrus streaming in from the west, expect mostly clear skies
to prevail overnight with winds turning light and variable.
Otherwise, expect winds to gradually ramp up after daybreak as they
become southeasterly, with gust between 20 to 25 kts possible at all
TAF sites tomorrow afternoon.




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